The present invention relates to a method for detecting invalid electronic storage media with individual identification information (ID) that is recognized as an invalid electronic storage medium and to a card system using the method. More particularly, the present invention relates to a method for detecting an invalid card in gate devices such as an automatic ticket gate wherein IC cards, or smart cards, are used, and to a technology that may conveniently be applied to a card system.
An electronic storage medium with individual identification information ID that is recognized as an invalid electronic storage medium is, for example, an invalid card. The invalid card refers to a card that has not yet expired but its use is prohibited because, for example, the user has lost the card.
Conventionally, a card is checked before use for validity to prevent the above-mentioned invalid card from being used.
The means that is in practical use today for detecting invalid cards include a method in which an inquiry about the validity of cards is sent to the host computer. For example, CAFIS (Credit And Finance Information System) is available for use as a method for checking the validity of cards issued from financial institutions.
As a means for detecting invalid cards without making an inquiry, there are also methods for detecting invalid cards by downloading a list of invalid IDs onto a terminal and then checking the list for a card that is to be examined. One of the methods which check the list for a card to be examined uses a hash function. The search method with the use of a hash function is disclosed, for example, in “Information Processing Handbook—New Edition”, Information Processing Society of Japan, pp. 99, Nov. 25, 1995.
In the method where a hash function is used for detecting invalid cards, a terminal or an IC card application unit reads an ID from an IC card and, for the IC card that was read, calculates a hash value using the predetermined hash function (This function performs an arithmetic operation for dividing IC cards into a predetermined groups according to the number of IC cards or the purpose of IC cards).
Then, the method checks the by-hash-value hot list (black list), which contains invalid IC card IDs classified by hash value, to see if the IC card to be checked is in the group corresponding to the calculated hash value. If the group corresponding to the hash value contains the ID of the IC card to be checked, the method performs invalid card processing; if the group corresponding to the hash value does not contain the ID of the IC card to be checked, the method performs valid card processing.
In this way, the method uses the hash function to calculate the hash value from the ID of an IC card. Then, it compares, one at a time, the IDs in the hash value group corresponding to the calculated hash value listed on the invalid card ID list with the ID of the card to be checked to detect if the IC card is an invalid card.